Embodiments herein relate generally to phase change ink compositions containing waxes and wax-soluble near-infrared (NIR) dyes, NIR prints made with such phase change ink compositions, and methods of producing a layer of such a phase change ink composition on the surface of a substrate. Some embodiments concern perimidine-squaric acid-based NIR dyes for hot-melt/phase change ink formulations.
Infrared (IR)/near-infrared (NIR) sensors and associated IR/NIR absorptive inks have been developed for tracking and authenticating a number of different objects. More specifically, labels, barcodes, or other identifiable markings formed from IR/NIR absorptive inks can be formed on the surface of a number of objects. Once marked, objects can be illuminated with IR/NIR light and examined by an infrared sensor to authenticate or track the object.
Some known IR/NIR dyes have visible color associated with them, causing the resulting dye-based IR/NIR inks and the printed matter to be visibly colored. Additionally, dye-based IR/NIR inks can have limited solubility in an ink base and low light fastness and environmental fastness (e.g., air, water, humidity, and thermal fastness). For example, pigmented IR/NIR absorptive inks can include carbon black as the IR/NIR absorptive material, resulting in a dark and highly visible ink. Consequently, some of the tracking and authentication effectiveness of the IR/NIR absorptive ink can be compromised.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in a liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of molten liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the printing media, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks for color printing generally comprise a phase change ink carrier composition, which is combined with a phase change ink compatible colorant or dye. Phase change inks often contain waxes, such as polyethylene wax.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long-term storage, and the like. Also, the problems associated with nozzle clogging due to ink evaporation related to other types of ink jet inks are largely eliminated, thereby improving the reliability of printing. Furthermore, in phase change ink jet printers where the ink droplets are applied directly onto the printing medium, the droplets can solidify immediately upon contact with the substrate. Thus, migration of ink along the printing medium is prevented and dot quality can be improved.
Phase change inks containing NIR inks would be useful for data coding and marking. Phase change ink formulations require thermally stable and wax-soluble dyes (NIR in this case) for use in the solid ink printers that operate with print-head temperatures of 110° C.-135° C. and higher.